Rapid-sweep electrochemical detector for chemical analysis of flow streams

Abstract

A system for identification and quantification of electrochemically active compounds in a flow stream involves stepping the electrode potential in a detector rapidly through the range of interest with a square wave superimposed on a staircase signal and recording the current response as functions of step number and sweep number, i.e., as functions of voltage and time. From the recorded data, a three-dimensional graph (potential, time and current) is structured and from which identification and quantification of the electrochemically active compounds is effected with minimum expenditure of time. The system includes a potentiostat controlled by a computer with, however, independent logic control contained in the potentiostat. Provision is also made to compensate automatically for variations in resistance between the cell electrodes.

We claim: 
     
       1. A data acquisition system comprising computer means and a measuring and control instrument, said instrument including analog circuit means for measuring at least one variable analog function with high sensitivity, an internal data bus, digital-to-analog converter means connected to said analog circuit means and fed by said internal data bus for changing the condition of said analog circuit means in accord with digital input to said digital-to-analog converter means, analog-to-digital converter means connected to said analog circuit means for converting the variable analog function being measured to digital format, an active data bus connected with said analog-to-digital converter means for periodically acquiring data therefrom corresponding to the measured analog function, and means interfaced between said active data bus and said internal data bus for sequentially applying digital input from said computer means to said digital-to-analog converter means and for grounding the internal bus to allow the analog function to be measured without being degraded by digital noise. 
     
     
       2. A data acquisition system as defined in claim 1 including graphics display means connected to said computer means for displaying said digital format on a real time basis. 
     
     
       3. A data acquisition system as defined in claim 1 wherein said analog circuit means is effective to detect Faradaic current in a flow stream which has been differentially eluted. 
     
     
       4. A data acquisition system as defined in claim 1 further including logic means for controlling said measuring and control instrument without control input from said computer means after initialization. 
     
     
       5. A data acquisition system as defined in claim 4 wherein said meauring and control instrument further includes an electrochemical detector having an electrochemical cell. 
     
     
       6. A data acquisition system as defined in claim 1 wherein said measuring and control instrument further includes an electrochemical detector having an electrochemical cell. 
     
     
       7. A data acquisition system as defined in claim 6 wherein said digital-to-analog converter means controls voltage level to said electrochemical cell. 
     
     
       8. A data acquisition system as defined in claim 7 wherein said analog circuit means include means for effecting IR compensation. 
     
     
       9. A data acquisition system comprising computer means and a measuring and control instrument, said instrument including analog circuit means for measuring at least one variable analog function with high sensitivity, logic means for controlling the measuring and control instrument, and an internal data bus as an input to said analog circuit means; an active data bus connected to said computer means; input means for sequentially connecting said active data bus as an input to said internal data bus and for grounding said internal data bus for a time sufficient to allow measurement with high sensitivity; and output means for repetitiously converting said variable analog function to digital format and for connecting said digital format to said active data bus. 
     
     
       10. A data acquisition system as defined in claim 9 including graphics displaya means connected to said computer means for displaying said digital format on a real time basis. 
     
     
       11. A data acquisition system as defined in claim 9 wherein said logic means controls the rate at which said digital format is output to said active data bus whereby the computer means is relieved of the burden of necessary capacity for so doing. 
     
     
       12. A data acquisition system as defined in claim 9 including an internal data bus connected to said analog circuit means for conditioning said analog circuit means, and means controlled by said logic means for causing isolating and grounding of said internal data bus at least during times in which analog measurement is taking place so that analog measurement is not degraded by digital background noise which would otherwise be present. 
     
     
       13. A data acquisition system as defined in claim 12 wherein said analog circuit means is effective to detect Faradaic current in a flow stream which has been differentially eluted. 
     
     
       14. A data acquisition system as defined in claim 12 including digital to analog converter means connected to said internal data bus for changing the condition of said analog circuit means, said means for isolating including means for activating said internal data bus between periods of analog measurement to allow changing the condition of said analog circuit means. 
     
     
       15. A data acquisition system as defined in claim 14 wherein said analog circuit means is effective to detect Faradaic current in a flow stream which has been differentially eluted. 
     
     
       16. A data acquisition system as defined in claim 12 including graphics display means connected to said computer means for displaying said digital format on a real time basis. 
     
     
       17. A data acquisition system as defined in claim 16 wherein said analog circuit means is effective to detect Faradaic current in a flow stream which has been differentially eluted.